Non-luminous display devices that use light emitted from an illumination device to perform a display include liquid crystal display devices, electrochromic display devices, and electrophoretic display devices. Among these, liquid crystal display devices are widely used, for example, in personal computers and mobile phones.
A liquid crystal display device applies a driving voltage to each of picture element electrodes regularly arranged in a matrix so as to change optical properties of a liquid crystal layer corresponding to an opening of the picture element. As a result, the liquid crystal display device displays images and characters thereon.
In a liquid crystal display device, TFTs (Thin Film Transistors), for example, are provided on a plurality of pixels as switching elements, respectively, in order to individually control the pixels. Also, lines are provided in order to supply a predetermined signal to the switching elements.
However, with a TFT (switching element) provided on each pixel, the luminance deteriorates since the pixel area decreases. Furthermore, the switching element and the line cannot be smaller than a certain size due to restrictions that arise from the electric properties and the manufacturing technology. An example of the restrictions arising from the manufacturing technology is the limitation of etching accuracy in photolithography in the order of 1 μm to 10 μm. Therefore, with development of a liquid crystal display device reduced in size with high definition, the following problem becomes significant: The smaller a pixel pitch, the lower open area ratios, and the lower luminance.
As a measure of solving the problem of a low luminance, there is a method in which a light-converging element is provided corresponding to each pixel in a liquid crystal display device so that light emitted from an illumination device is converted onto a transparent region of each pixel. For example, Patent Document 1 discloses a semi-transmissive (transmissive-reflective) liquid crystal display device having a transparent region and a reflective region, wherein a light-converging element such as a microlens is provided.
A semi-transmissive liquid crystal display device has been developed in recent years to be used suitably in a bright environment for mobile phones, for example. A semi-transmissive liquid crystal display device has a pixel including (a) a transparent region that performs a display in a transmissive mode with the use of light emitted from a backlight, and (b) a reflective region that performs a display in a reflective mode with the use of ambient light. Display can be performed in the transmissive mode, the reflective mode, or both modes together, depending on the environment in which the liquid crystal display device is used.
In such a semi-transparent liquid crystal display device, a reflective region needs to be large to some extent so that a predetermined brightness is secured in performing a display reflectively. This results in decrease in area ratio of the transmissive region to the pixel, thus decreasing luminance in the transmissive mode.
Patent Documents 1 and 2 disclose a method for converging light with a high degree of efficiency. According to the method, a semi-transmissive liquid crystal display device includes (i) a reflective plate having an opening and (ii) a light-converging element, such as a microlens, both of which are provided on one surface of a substrate disposed on the backlight side, which surface is on the liquid crystal side. As a result, light which is projected from the backlight into the microlens is converged onto an opening provided on the reflective plate.
According to the arrangement described in Patent Document 2, the reflective plate and the microlens are disposed on the same surface of the substrate and on the liquid crystal side. This makes it possible to contain the reflective plate inside, optimize a distance between the microlens and the reflective plate, and fine alignment between the opening of the reflective plate and the microlens.
Patent Document 3 discloses the following method for increasing light conversion efficiently. According to the method, the base of a microlens is circular or hexagonal. The microlenses and transmissive regions of pixels are arranged in a staggered pattern, and the microlenses are in a one-to-one correspondence with the transmissive regions. Further, the focal point of the microlens is placed at the center of the transmissive region of the pixel. As a result, light-converging efficiency of the microlens (efficiency in utilization of light projected from an illumination device) is improved.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 11-109417 (published on Apr. 23, 1999)    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2002-333619 (published on Nov. 22, 2002)    Patent Document 3. Japanese Unexamined Patent Application Publication No. 2003-255318 (publicized on Sep. 10, 2003)